Many electronic devices incorporate baffles to produce known electrical effect within the associated device. Examples are found in resonant microwave cavities, terminations and deflectors in waveguides and other such transmission lines, and in transmit-receive protectors in radars. Baffles are usually adjusted or changed manually or mechanically to adjust an electronic characteristic of the associated device. However, there are circumstances in which a remotely controlled and rapidly changeable baffle should prove a more significant and highly desirable asset.
The frequency of a Klystron tube, commonly used in radars to generate or amplify microwave signals, may be rapidly changed by altering the size of its tuning cavity using a movable baffle. That effect was earlier recognized by Klotz in U.S. Pat. No. 3,471,811, granted Oct. 7, 1969, which describes tuning a microwave cavity using an electrically operated piezoelectric mechanism to physically position a metal wall, by Perkins et al in U.S. Pat. No. 3,478,246, granted Nov. 11, 1969 and also by Hull in U.S. Pat. No. 3,478,247, granted Nov. 11, 1969, wherein a coaxial magnetron tube incorporates a piezoelectric mechanism to rapidly mechanically position a cavity wall to provide frequency tuning of the magnetron. Although electronic in nature, at a more microscopic view, such tuning is somewhat mechanical in nature in that an electrically conductive metal coating or layer is physically moved by the piezoelectric mechanism. An advantage to tunable microwave cavities that incorporate the present invention is that microwave cavities may be tuned without mechanical movement of the tuning element.
Radar TR switches are another example. When the transmitter and receiver are connected to a common antenna, as is typical for many radars, the highly sensitive receiver must be protected from the high power RF that is generated by the transmitter during transmission of that RF power to the antenna. That protection is provided by a transmit-receive protector, an electronic device generally referred to simply as a TR switch, and which acts as an electronic gate. In operation, when the radar transmitter generates RF, the TR switch short circuits the antenna inputs to the receiver, effectively closing the gate to the receiver. In the intervening periods when the transmitter is not applying RF to the antenna, the TR switch opens the RF signal path to the receiver, allowing any low power RF received at the antenna to propagate to the receiver.
Typical TR switches are formed of either a solid state switching device or a gas tube, which is connected in shunt of the receiver's input. With the gas tube, when the transmitter is generating RF, the voltage on the line from the transmitter is high, and the gas in the tube consequently ionizes and conducts current, thereby short circuiting the receiver input and protecting the receiver. The present invention provides a new form of TR switch that requires neither gas tubes or semiconductor switches.
Accordingly, an object of the invention is to provide a new form of electronic baffle for use in microwave devices.
Another object of the invention is to provide improved electronic tuning for microwave devices that may be easily controlled by remotely located controls.
Still another object is to provide an improved TR switch for radar systems that does not use gas tubes or semiconductor switches.
And an ancillary object of the invention is to provide an improved RF transmitting antenna that minimizes the generation of side and back lobes.